The present invention relates to a transmission power distribution method and reception method and a signal to be used at wireless stations of a wireless communication system; and, more particularly, the invention relates to a communication system, transmitting station, and receiving station that use error correcting codes.
A known technology for controlling a wireless communication device's transmission power is available for achieving a desired reception quality for a wireless communication system. For example, U.S. Pat. No. 5,267,262 discloses a technology for allowing a base station of a CDMA mobile communication system to measure the signal reception power from a terminal and to issue a transmission power increase instruction to a mobile station when the measured power value is smaller than a desired value, or to issue a transmission power decrease instruction to a mobile station when the measured power value is greater than a desired value, so as to permit the mobile station to control the transmission power in compliance with the above-mentioned transmission power control instruction, thereby ensuring that the power received by the base station is virtually constant.
Another technology, which is disclosed by U.S. Pat. No. 5,559,790, has a mobile station measure the reception quality of a pilot signal transmitted by a base station at a known power level and transmit a transmission power control signal to the base station in accordance with the measured reception quality, so as to request a higher transmission power when the reception quality is poorer than when the reception quality is adequate. Thus, the base station is able to control the transmission power for a signal directed to the mobile station in accordance with the received transmission power control signal, thereby ensuring that the quality of a signal received from the base station is maintained virtually constant for the mobile station.
The above technologies make it possible to provide a consistent reception quality by maintaining the power received by a receiving station constant and to avoid reception quality deterioration due to a channel gain fluctuation and intra-system interference due to an unduly high transmission power. To maintain the reception quality constant, however, it is necessary to send transmissions at a high transmission power level depending on a temporary decrease in the channel gain. Such temporary high transmission power causes interference with other communications.
Another technology, which is disclosed by JP-A No. 215219/1998, temporarily stops transmission to prevent other communications from being interfered with by unduly high transmission power when the transmission power exceeds a predefined reference level as a result of control for reception quality maintenance.
To increase the maximum number of simultaneous communications, it is necessary to reduce the transmission power for individual communications to the fullest possible extent, thereby minimizing interference with the other communications.
The conventional technologies, however, have been developed to increase the communication stability by maintaining the reception quality constant during communications. This means that the transmission power needs to be increased if the channel quality is poor. This sets a limit on the decrease in the transmission power when using the conventional technologies.